Marriage is a union of man to a woman. When people marry for love, there is no dout that family will be happy. It is impossible to love several women at the same time. Loving somebody is almost the same to treat him or her failry. In my opinion, polygamy will be obstacle for it. Can you imagine a life children from different mothers? Do the friendship and respect exist among them? It may, but very rare, right? Children are born to be happy, not suffer from abuses of stepbrother and sisters. I am meantioning this, because nowadays victimis of sibling abuse have increased. If we legalise the polygamy, the situation will be worse.

The ability to marry people who are already married presents us with the chance to take partners that have already proven themselves in society as responsible parents and providers - that is, to reduce the risk in marriage. It also means that one doesn't have to settle for those "left over"; you can marry the person you want, not just the person that's left. Very few countries have exactly the same number of males and females; in the UAE, there are 2.2 males per female, but in Estonia, there are only 0.84 males per female1. This means that monogamy restricts options significantly.

Wow, you guys are coming at this from a strange angle. The question uses 'should' indicating that this is an ethical debate as well as a legal debate. It isn't clear which country we are talking about, I assume America, where polygamy is illegal almost everywhere if not everywhere. One thing we must recognize is the term 'polygamy' can refer to either polygyny, multiple wives or polyandry, multiple husbands. I'm not sure what you would call it if there were multiple wives and husbands together if some were bisexual. Leaving aside the seemingly unrelated topics of sibling abuse and problems of unevenly gendered populations, the ethical question rephrased is, "Is there good enough reason for the government take away people's freedom to marry in such a manner?" If that isn't what you two wish to debate, please title your debate more accurately. Thanks and good luck to each of you.